With the advent and propagation of various devices such as smartphones, tablet PCs, etc. and technologies which require machine-to-machine (M2M) communication and high data throughput, the quantity of data that needs to be processed in a cellular network has rapidly increased. To satisfy rapidly increasing data throughput, carrier aggregation, cognitive radio technology, etc. for efficiently using a wider frequency band and multiple-input multiple-output (MIMO), cooperative multi-point (CoMP), etc. for increasing data throughput within a limited frequency band have been developed. Furthermore, communication environments are evolved such that the density of nodes which can be accessed by a user equipment (UE) increases. A node refers to a fixed point including one or more antennas and capable of transmitting/receiving radio signals to/from a UE. A communication system including high-density nodes can provide high performance communication services to UEs according to cooperation between nodes.
CoMP communication in which a plurality of nodes communicates with a UE using the same time-frequency domain has data throughput much higher than that of a conventional communication scheme in which each node operates as an independent base station (BS) to perform communication with a UE without cooperation.
A multi-node system performs cooperative communication using plural nodes each of which operates as a BS, access point, antenna, antenna group, radio remote header (RRH) or radio remote unit (RRU). The plural nodes are spaced apart from one another by a predetermined distance or more in the multi-node system, unlike a conventional centralized antenna system in which antennas are concentrated in a BS. The plural nodes can be managed by one or more BSs or BS controllers which control operation of each node or schedule data to be transmitted/received through each node. Each node is connected to a BS or a BS controller which manages the corresponding node via a cable or a dedicated line.
The multi-node system can be regarded as a MIMO system since distributed nodes can communicate with one or more UEs by simultaneously transmitting/receiving different streams. However, in the multi-node system, a transmission area that needs to be covered by each antenna is reduced, compared to an area covered by each antenna included in the conventional centralized antenna system, because signals are transmitted using nodes distributed in a plurality of locations. Accordingly, the multi-node system can reduce power necessary for each antenna to transmit a signal compared to a conventional centralized antenna system employing MIMO. Furthermore, a transmission distance between an antenna and a UE is reduced and thus path loss is decreased and fast data transmission is enabled. Therefore, throughput and power efficiency of a cellular system can be improved and communication performance with relatively uniform quality can be satisfied irrespective of the position of a UE in a cell. In addition, in the multi-node system, BSs or BS controllers connected to plural nodes cooperatively transmit/receive data so as to reduce signal loss during signal transmission. Moreover, when nodes spaced apart from one another perform cooperative communication with a UE, inter-antenna correlation and interference are reduced. Therefore, according to the CoMP communication scheme, a high signal-to-interference-plus-noise ratio (SINR) can be obtained.
Owing to the above-mentioned advantages of the multi-node system, the multi-node system replaces the conventional centralized antenna system or is employed along with the centralized antenna system as a new cellular communication system in order to reduce BS establishment costs and backhaul network maintenance costs in next-generation mobile communication systems, extend service coverage and increase channel capacity and SINR.